1. Field of the Invention
The present invention relates to a semiconductor light-emitting element using an InGaAlP system mixed crystal with a high brightness as a Light Emitting Layer in a LED, and a method for fabricating this semiconductor light-emitting element, and, in particular, to a semiconductor light-emitting element with superior resistance to humidity and with a long life expectancy providing high output performance, and a method for fabricating this semiconductor light-emitting element.
2. Description of the Prior Art
In recent years an Light Emitting Diode (LED) has been developed with a light-emitting layer of an InGaAlP mixed crystal system, as a high brilliant LED. The use of a Ga.sub.1-x Al.sub.x As current spreading layer, as a current diffusion layer, with a high ratio of mixed Al crystals (hereinafter X.sub.Al) on the light producing surface is a structural feature of this LED. (Hereinafter there will be cases where, for brevity, when the ratio of included Al is high, the term "high Al" will be used, and when this ratio is low, the term "low Al" will be used.)
FIG.1 is a general sectional view of an orange colored light-emitting InGaAlP LED formed using conventional technology.
For example, with epitaxial growth of a yellow light-emitting InGaAlP LED used as an example, as illustrated in FIG. 1, an n-type In.sub.0.5 (Ga.sub.0.3 Al.sub.0.7).sub.0.5 P-clad layer 2 with a film thickness of 1.0 .mu.m fabricated by a metal organic chemical vapor deposition method (MOCVD method) is formed on an n-type GaAs substrate 1, and then, an n-type In.sub.0.5 (Ga.sub.0.72 Al.sub.0.28).sub.0.5 P active layer 3 with a film thickness of 0.5 .mu.m, a P-type In.sub.0.5 (Ga.sub.0.3 Al.sub.0.7).sub.0.5 P-clad layer 4 with a film thickness of 1.0 .mu.m, and a P-type Ga.sub.0.2 Al.sub.0.8 As current spreading layer 5 with a film thickness of 10 .mu.m are successively formed, respectively. Subsequently, an electrode 7 is formed on the P-type Ga.sub.0.2 Al.sub.0.8 As current diffusing layer 5 and an electrode 8 is formed on the other side of the n-type GaAs substrate 1. Finally, an element is detached by means of a dicing process to obtain an LED pellet.
In this manner, a high Al mixed crystal ratio X.sub.Al of 0.8 is obtained for a pellet light producing surface of the GaAlAs layer 5.
However, this type of GaAlAs layer 5 with a high Al mixed crystal ratio has a tendency to oxidize very easily, and for this reason the light-emitting characteristics deteriorate. This causes an extreme reduction in the life expectancy of the element, and the same drawback is also found in an element sealed in plastic.
As a countermeasure, conventionally, a method for forming a natural oxidation film has been carried out using a chemical surface treatment as another chemical process (for example, wet etching using a mixed reagent of NH.sub.4 OH and H.sub.2 O.sub.2), but the natural oxidation film obtained by this method is highly irregular, and the close adherence characteristics are weak because the oxidized film is formed forcibly. Because this film lacks mechanical strength, variations are produced in the life expectency.
In addition, because of the character of this chemical process, problems arise inasmuch as it is not possible to carry out the process for forming the above-mentioned layers 1, 2, 3.4, and 5 continuously, and, for this reason, the manufacturing takes considerable time.
Also, because of the character of a protective film of SiO.sub.2 or SiN.sub.x, usually formed by manufacturing using a silicon element, it is not possible to carry out the process For forming the above-mentioned layers 1, 2, 3, 4, and 5 successively, therefore there is the problem that the cost of manufacturing is increased.
If the Al mixed crystal ratio X.sub.Al for the Ga.sub.1-x Al.sub.x As current diffusing layer 5 is reduced to 0.5 or less during the formation of the layer, the life expectancy of the element is improved, but, conversely, there is a large absorption ratio for the light-emitting wave lengths from red to green, therefore this is not practical.
As outlined above, with a conventional semiconductor light-emitting element and tile method for fabricating this element, a GaAlAs layer with a high Al mixed crystal ratio which is used as a current diffusing layer is very easily oxidized, therefore the light-emitting characteristics deteriorate, causing an extreme reduction in the life expectancy of the element.
In order to solve this problem, the natural oxidation film obtained by this method is highly irregular, even when a method to form a natural oxidation film using a chemical process is utilized, and this film lacks mechanical strength. There is therefore the drawback that variations are produced in the life expectancy. In addition, this chemical surface process requires another process in addition to the formation of each layer of the semiconductor light-emitting element. There is therefore the problem that excessive time is required for fabricating.